The preparation of overbased calcium salts of carboxylic acids, alkyl phenols, and sulfonic acids are disclosed in the U.S. Pat. Nos. 2,616,904; 2,760,970; 2,767,164; 2,798,852; 2,802,816; 3,027,325; 3,031,284; 3,342,733; 3,533,975; 3,773,664; and 3,779,922. As described therein, the widely used overbased calcium soaps are either salts of alkylarylsulphonic acids, oleic acid, naphthenic acids, or branched saturated oxo-acids of C7 to C25 hydrocarbons.
U.S. Pat. Nos. 2,865,956; 2,938,828; and 4,100,084 report various methods of producing calcium naphthenates. These products often have relatively slow filtration rates and contain considerable amounts of solids, predominantly non-dispersible, agglomerated calcium carbonate particles which require measures for their removal. The overbased naphthenates are often dark in color which limits their use in applications where discoloration is a problem, such as in paints and coatings. The preparation of these compounds typically involves two reactions and can be summarized as follows:
1) Preparation of Calcium Naphthenate:2RCO2H+M(OH)2→(RCOO)2M+H2O2) Overbasing:(RCOO)2M+XM(OH)2→(RCOO)2Mx+MCO3 In which:    M is a metal    X ranges from 1 to 10    R is a hydrocarbyl radical of 15 to 40 carbon atoms.    Step 2 takes place in the presence of CO2 gas and a solvent.
The preparation of the overbased salts using alkylarylsulphonic acid is a difficult process. Typically the process involves the reaction the alkylarylsulphonic acid with a metal oxide or hydroxide in a suitable solvent.
U.S. Pat. No. 4,225,509 teaches an overbased alkaline earth metal hydrocarbyl sulfonate which is made in the presence of carbon dioxide (CO2) and promoters. The promoters are usually labile hydrogen compounds such as phenols, alcohols and amino-alcohols. Products prepared by such method have dark colors and it is difficult for them to reach high metal content.
U.S. Pat. No. 4,597,880 discloses a one-step process for preparation of overbased calcium sulfonate greases. The essential ingredients include a mixture of a liquid carrier, a sulfonic acid, calcium oxide or hydroxide, water-soluble carboxylic acids, preferably an alcohol or alkoxyalcohol of 1 to 8 carbon atoms, and water, wherein the mixture is carbonated. Calcium soaps from this method of preparation cannot be used in paint applications because of dark color.
In U.S. Pat. No. 4,824,585, overbased calcium soaps having a basicity of about 4 are described which overcome the disadvantages of the known soaps and which yield stable and clear solutions in oil. As used above and throughout this application, basicity is the total amount of calcium in a product divided by the amount of calcium linked to carboxylic acid compounds. The products described in this patent are made by carbonation of excess of calcium hydroxide dispersed in a reaction medium containing an oil-soluble organic acid, a hydrocarbon solvent, a low molecular weight alcohol, and mineral oil, followed by filtration of the unreacted materials. Carbonation is carried out in the presence of catalysts such as metal oxides and zinc carboxylates and promoters of higher alcohols, glycols, alky-phenols or amines. These compounds remain in the finished product and the presence of the catalyst and oil in the finished product can limit its use.
In the U.S. Pat. Nos. 4,824,585, 5,501,807 and 5,830,832, high basicity calcium soaps are obtained by carbonating a mixture of a C7 to C15 carboxylic acid, which is preferably a branched chain oxo-acid in the presence of excess calcium and a volatile solvent at a temperature from 15° to 60° C. Products with basicity of 4 to 8 may be obtained. These patents teach the use of saturated oxo-acids in high concentrations in the range of 50% or more by weight, and of using mono-or poly-substitution on carbon 3 or higher of the carboxylic acid. These patents limit the percentage of acids branched on carbon 2 to between 0% and 20% by weight of the total acid.
Several unsuccessful examples have been reported wherein a high percentage of the acid substituted on carbon 2 was used. To the knowledge of the present inventors, carboxylic acids with carbon numbers less than 7 have not been proposed for use in the preparation of overbased calcium soaps.